The purpose of the symbol test case is to create some symbols and then
have them rendered when instantiated by the use element. This file
contains 3 symbol definitions. Only two are ever rendered. There
is a viewport defined to be 0,0,1000,1000 on the svg element. Each
symbol has is own viewport of the same dimensions. The symbols are
scaled when they are instantiated by the use element, The first set
of symbols is 4 squares, red and yellow in color they should appear
in the lower right of the view arranged in a checkerboard fashion.
The second symbol to be used is an image which should appear in the
upper left of the view area. The symbol that is not used and should
not be rendered is a large black rectangle. If the symbols don't
appear, there is something askew with the use statement, if they
appear but either overlap each other or in some way aren't in the
correct positions they have not honored either their viewport or
were not scaled when placed by the use element in the area defined by
it. If everything is black then perhaps a symbol was rendered that
should not have been.

The rendered picture should match the reference image, except for possible
variations in the labelling text (per CSS2 rules).